feat(mall): classic B2B2C PC storefront with fixed mock API layer

- Mock adapter implementing @vmall/shared ApiClient (localStorage-persisted
  cart/orders/invoices), runtime switch via mockApi flag (default on)
- Fixed bilingual mock catalog: 3-level categories, 24 products w/ SKUs,
  stores, brands, banners, floors, seckill/collective/integral, comments,
  coupons, addresses, seeded orders/shipments/invoices
- B2B2C mall shell: top bar, logo/search/cart header, dark nav + category
  mega-menu, value-prop footer, back-to-top; 1200px grid, #ca151e theme
- UI primitives replacing element-plus: carousel, pagination, breadcrumb,
  qty stepper, rating stars, modal, tabs, step bar, product card
- Pages: home floors, search (filters/sort/paging), goods detail (SKU
  picker, store rail, review tabs), cart -> checkout -> pay -> success,
  auth pages, user center (dashboard/orders/addresses/favorites/coupons/
  invoices), stores, seckill, collective, integral
- i18n split into per-domain locale modules (en+zh)
- OpenSpec change mall-pc-storefront-replica archived; all specs green

apps/mall/components/ui/Modal.vue

@@ -0,0 +1,65 @@
+<script setup lang="ts">
+defineProps<{ open: boolean; title?: string }>();
+const emit = defineEmits<{ close: [] }>();
+</script>
+
+<template>
+  <Teleport to="body">
+    <div v-if="open" class="mask" @click.self="emit('close')">
+      <div class="dialog">
+        <header v-if="title" class="head">
+          <span>{{ title }}</span>
+          <button type="button" class="x" :aria-label="$t('common.cancel')" @click="emit('close')">×</button>
+        </header>
+        <div class="body">
+          <slot />
+        </div>
+        <footer v-if="$slots.footer" class="foot">
+          <slot name="footer" />
+        </footer>
+      </div>
+    </div>
+  </Teleport>
+</template>
+
+<style scoped>
+.mask {
+  position: fixed;
+  inset: 0;
+  background: rgba(0, 0, 0, 0.4);
+  z-index: 900;
+  display: flex;
+  align-items: center;
+  justify-content: center;
+}
+.dialog {
+  background: #fff;
+  min-width: 420px;
+  max-width: 720px;
+  border-radius: 4px;
+  box-shadow: var(--mall-shadow);
+}
+.head {
+  display: flex;
+  justify-content: space-between;
+  align-items: center;
+  padding: 14px 20px;
+  border-bottom: 1px solid var(--mall-line);
+  font-size: 15px;
+}
+.x {
+  border: 0;
+  background: none;
+  font-size: 20px;
+  cursor: pointer;
+  color: var(--mall-muted);
+}
+.body {
+  padding: 20px;
+}
+.foot {
+  padding: 12px 20px;
+  border-top: 1px solid var(--mall-line);
+  text-align: right;
+}
+</style>